The present invention relates to a gaseous discharge plasma display panel, which providss a flat and thin display screen. In particular, the present invention relates to such a panel which provides a high density of display cells for excellent picture quality, and high speed scanning operation.
In a conventional matrix type plasma display panel, a plurality of row electrodes and a plurality of column electrodes are arranged so that they cross perpendicular to one another to provide a display cell at each cross point. Upon applying potential between electrodes, the cell defined by the electrodes with the potential discharges and glows to display a bright dot of a character or a picture pattern. A display is accomplished through conventional scanning technique. There have been known two kinds of plasma display panels, an AC (alternate current) type, and DC (direct current), type. In the former type plasma display panel, the electrodes are covered with the dielectric layer, and a cell is energized by AC current. The AC type plasma display panel has the feature that a cell itself memorizes an indication information and so no external refresh memory is requested. In the latter DC type plasma display panel, the electrodes are disposed directly in a gaseous atmosphere without dielectric cover, and is energized by DC current. Although a DC type plasma display panel must have an external refresh memory, it has the advantage that an external circuit for operating the panel may be small and simple as compared with that of an AC type panel. The present invention relates in particular to a DC type plasma display panel.
One of the requests for a plasma display panel is high scanning speed, or quick firing of a discharge cell of a panel. That high speed scanning operation is essential in particular when there are provided a plenty of cells and a field frequency (refresh frequency) is high.
A prior art for quick firing of a cell for a DC type plasma display panel has been shown in U.S. Pat. No. 3,644,925, which has auxiliary speed cells in a panel. The seed cell glows continuously at a low level, not for viewing, but to provide excited particles for firing the indication cells. Due to the presence of ions or excited particles in gaseous cells, a quick firing of a cell which is located close to a seed cell is accomplished. In a practical structure for high speed scanning operation panel, the seed cells and the indication cells are positioned alternately so that any indication cell or display cell has an adjacent seed cell which provides excited ions or particles for firing said indication cell.
The prior plasma display panel with the seed cells and its operation are described in accordance with FIGS. 1A through 1D for the sake of the easy understanding of the present invention.
FIG. 1A is a cross section of the prior plasma display panel, FIG. 1B is the cross section at the line A--A of FIG. 1A, FIG. 1C shows the circuit diagram for operating the plasma display panel of FIG. 1A, and FIG. 1D shows operational waveforms in the circuit of FIG. 1C.
In FIGS. 1A and 1B, a plurality of parallel column display electrodes 1 and a plurality of auxiliary seed electrodes 2 are mounted in elongated ditches provided on a back support panel 3. A plurality of row electrodes 4 are positioned perpendicular to those column electrodes 1 and those seed electrodes 2. A transparent cover glass 6 covers all the electrodes. The cover glass 6 has elongated ditches 5 which provide a discharge space, and opaque black blind portion 7 along the seed electrodes 2. The column electrode 1 is called an anode electrode, and the row electrode 2 is called a cathode electrode, since the former is coupled with an anode of a power source, and the latter is coupled with a cathode of a power source.
In FIG. 1C, the anode electrodes (Y.sub.1, Y.sub.2, Y.sub.3) and the seed electrodes (S.sub.1, S.sub.2) are positioned alternately so that they are perpendicular to the cathode electrodes (X.sub.1, X.sub.2, X.sub.3). The cathode electrodes (X.sub.1, X.sub.2, X.sub.3) are supplied either the ground potential or the predetermined potential V.sub.b through the switches (SX.sub.1, SX.sub.2, SX.sub.3) which are controlled by the output of the decoder. The decoder receives the output of the counter which receives a clock pulse, and provides the control signals (T.sub.x1, T.sub.x2, T.sub.x3) alternately to said switches. When the control signal (T.sub.x1, T.sub.x2, T.sub.x3) is active, the related cathode electrode (X.sub.1, X.sub.2, X.sub.3) is grounded. The anode electrodes (Y.sub.1, Y.sub.2, Y.sub.3) are coupled with the power source V.sub.a through the resistors R.sub.1, and the junction point of said resistor R.sub.1 and the anode electrode is grounded through a resistor R.sub.2 and a switch (SY.sub.1, SY.sub.2, SY.sub.3) controlled by pattern data through the buffer circuit. When the switch (SY.sub.1, SY.sub.2, SY.sub.3) is open, the potential of the anode electrode is V.sub.a (high potential), while the switch (SY.sub.1, SY.sub.2, SY.sub.3) is closed, the potential of the anode electrode is low potential which is defined by the resistors R.sub.1 and R.sub.2. A cell discharges and glows only when the related anode electrode is on high potential V.sub.a, and the related cathode electrode is grounded. The seed electrodes (S.sub.1, S.sub.2) are coupled with the potential V.sub.a through the resistor R.sub.1, therefore, those seed electrodes have the potential V.sub.a irrespective of pattern data.
FIG. 1D shows operational time sequence of the circuit of FIG. 1C, where it is assumed that each frame period has three timing clock durations (t.sub.0, t.sub.1, t.sub.2). The cathode electrodes (X.sub.1, X.sub.2, X.sub.3) are provided the potential (V.sub.x1,V.sub.x2, V.sub.x3), which is grounded alternately as shown by the shaded area in FIG. 1D. On the other hand, since the seed electrodes (S.sub.1, S.sub.2) always provide the high voltage V.sub.a through the resistors R.sub.1, the seed current (I.sub.s1, I.sub.s2) flows continuously as shown in FIG. 1D. That is to say, when the first cathode electrode X.sub.1 is grounded, the cell (X.sub.1 -S.sub.1) between the cathode electrode X.sub.1 and the seed electrode S.sub.1 is active, and the current flows through that cell. Similarly, the seed cell (X.sub.1 -S.sub.2) is active. Next, when the second cathode electrode X.sub.2 is grounded at the timing t.sub.1, the cells (X.sub.2 -S.sub.1) and (X.sub. 2 -S.sub.2) are active. Similarly, when the third cathode electrode X.sub.3 is grounded, the seed cells (X.sub.3 -S.sub.1) and (X.sub.3 -S.sub.2) are active.
At the clock timing t.sub.0, the anode electrode Y.sub.2 is at high voltage, and other anode electrodes Y.sub.1 and Y.sub.3 are at low voltage. Therefore, only the cell (X.sub.1 -Y.sub.1) glows. It should be appreciated in that case that the seed cells (X.sub.1 -S.sub.1) and (X.sub.2 -S.sub.2) are active at the clock timing t.sub.0, and there are many ions on charged particles near those active seed cells. Therefore, when the firing potential is applied to the display cell (X.sub.1 -Y.sub.2), said cell fires quickly by the seed effect of the adjacent low glowing seed cells.
At the clock timing t.sub.1, the seed cells (X.sub.1 -S.sub.1) and (X.sub.1 -S.sub.2) stop, but remain many charged ions near those cells. Therefore, when the potential is applied to the seed cells (X.sub.2 -S.sub.1) and (X.sub.2 -S.sub.2) which is located close to said seed cells (X.sub.1 -S.sub.1) and (X.sub.1 -S.sub.2), those seed cells (X.sub.2 -S.sub.1) and (X.sub.2 -S.sub.2) fire quickly at the clock timing t.sub.1. Similarly, the display cells (X.sub.2 -Y.sub.1) and (X.sub.2 -Y.sub.2) fire quickly by the seed effect of the seed cells. Similarly, at the clock timing t.sub.2, the seed cells (X.sub.3 -S.sub.1) and (X.sub.3 -S.sub.2), and the display cell (X.sub.3 -Y.sub.3) fire. Of course, the bright display cells are determined by the pattern data applied to the anode electrodes.
Accordingly, it should be appreciated that the discharge of a seed cell shifts along a seed electrode, and similary, the discharge of a display cell shifts along an anode electrode. A display cell is fired quickly due to the presence of a seed cell.
However, the prior plasma display panel as described has the disadvantage due to the presence of the seed electrodes that the density of the display cells can not be high enough for high picture quality with high resolution power. It should be noted that the space between the electrodes is restricted by the manufacturing process. So, if there were no seed electrode, the space between the anode electrodes would be halved, or the density of the anode electrodes would be doubled.